1. Field of the Invention
The present invention relates to novel seismic survey data acquisition equipment design; and also to seismic survey methods utilizing the uniquely designed and manufactured equipment. In particular, the invention relates to seismic survey cable connector design, equipment assembly combinations, the methods of equipment deployment, and operation of equipment.
2. Description of Related Art
In principle, a seismic survey represents a voluminous data set containing detailed information that may be analyzed to describe the earth's layered geology as indicated by seismic wave reflections from acoustic impedance discontinuities at the layer interfaces. The analysis is influenced by elastic wave propagation velocities respective to the differences in strata density or elasticity. A seismic event such as is caused by the ignition of buried explosives in a shallow borehole or by a vibratory mechanism placed at the earth's surface is launched into the earth at a precisely known location and time. Seismic waves propagating away from this original man-made seismic event are detected by a multiplicity of analog or digital sensors characterized in the art as geophones and/or hydrophones. Arrays of such sensors are distributed in a more or less orderly grid over the area of interest. The location of each sensor array is precisely mapped relative to the location of the seismic event. As the seismic wave from the timed event travels out from the source, reflections and other emanations from that original seismic wave are returned to the surface where they are detected by the sensors. The sensors respond to the receipt of a wave with a corresponding analog or digital electrical signal. There may be an array of individual sensor units that are combined in a physical circuit to provide a one time-variant signal to a data acquisition module on a sensor signal channel. One or more channels are received by a digital-signal-processing/communication module, called remote acquisition module (RAM) in this document. The RAM digitizes the analog signal streams for retransmission toward a central recording unit (CRU). If digital sensors instead of analog sensors are utilized, the RAM is not required to digitize the signals but must still perform other duties including retransmission of the signals toward the CRU. Among the significant data transmitted by a RAM or digital sensor may be the amplitude or strength of the reflected wave. The exact time lapse between the moment the event occurred and the moment the analog value of the sensor or sensor array is translated to a digital value may be digitized or it may be determined implicitly by position of the sample within a data stream.
In a single survey, there may be many thousands of sensor signal sources. Consequently, the data flow must be orderly and organized. Managing an orderly flow of this massive quantity of data the CRU, often in a field survey truck, requires a plurality of RAMs and other digital signal processing devices. The RAMs and other digital signal processing devices may be connected by cables for the purpose of data transmission toward the CRU and communication of control signals and other information in both directions, toward and away from the CRU. The system controller within the CRU may define and operate a communication network that includes all of the devices variously connected. In one example of such a system, RAMs may be connected by cable sections to form a receiver-line. Multiple receiver-lines may typically be connected to a base-line via digital-signal-processing/communication devices that may be called base-line units (BLUs). The base-line may consist of multiple cable sections connected by a series of BLUs and ultimately to the central recording unit (CRU) that includes the system controller. A RAM may receive the analog or digital sensor data from a multiplicity of sensors or sensor arrays and, in the case of analog sensors, converts the analog data to digital data. The RAM may then transmit the digital data, in the form of data packets, along its receiver-line. Transmissions may be to the adjacent RAM which relays the received information to the next proximate RAM, which in turn relays the data onward. At the point where the receiver-line connects to a base-line, the connecting BLU receives the transmission of all of the data from the series of RAMs in that receiver-line as transmitted to it from the nearest RAM; transmissions along the base-line proceed from BLU to BLU and finally to the CRU.
Commands and information from the CRU travel the reverse path to the point where they are received by the intended BLU or CRU. There may be many RAMs transmitting respective data packets along a single receiver-line. Typically, two or more receiver-lines connect with a BLU that further coordinates the data packet flow along the base-line. Numerous additional BLUs, connecting sections of the base-line and joining receiver-lines to the base-line, receive and retransmit data for ultimate receipt by the CRU.
Seismic surveying is often carried out under extremely inhospitable conditions of heat or cold, tropics or arctic, land or sea, desert or swamp. Necessarily, manual placement of the sensors, data acquisition units, base-line units, receiver-line cables and base-line cables is normally required.
One of the many challenges facing seismic ground crews using cable-connected systems is the initial decision of cable configuration(s). Data demands by geologists and investors are not always predictable. Seismic contractors must try to choose cable configurations that minimize weight and complexity for their workers in the field while keeping the number and type of cables and cable connectors to a minimum.
Prior art seismic systems have been designed to use two receiver-line cable sections between each pair of RAMs with takeout connectors for each sensor array. The cables may have, for example, four (4) takeout connectors per cable section, allowing attachment of four sensor arrays. With two cable sections connecting to each RAM a total of eight (8) channels of sensor arrays is connected to the RAM (four from each side) in this example. The cable itself contains at least enough conductors to accommodate the four sensor arrays (two conductors per array) plus the communication of data and commands along the receiver-line.
The prior art approach requires that the cable connectors at the two ends of the receiver-line cable section be either (1) be of two different types; or (2) be of the same type, and if so, at the end connected to the adjoining cable, be combined with an adapter called a back-to-back connector. The undesirable features of the prior art have been necessitated by the requirement that, at the RAM end of the cable section, its sensor channels must electrically connect to the RAM, whereas at the opposite end (midway between two RAMs) there must be no electrical connection of the sensor channels. (If the sensor channels were in fact connected, two physically distinct sensor arrays would be inadvertently combined.) The prior art designs in either case (1) or (2) add to the complexity and cost of manufacturing the cables and connectors. The added complexity also seriously impacts the operational cost of system utilization. In case (1), when deploying the system in the field, the directionality of the cables sections means they must be laid onto the ground in the correct direction; and if a mistake is made the cable section must be picked up and laid a second time, in the opposite direction. In case (2) the back-to-back connector is an additional equipment item that must either be carried separately or strapped to both ends of the cable and used only for the mid-way cable-to-cable connection. This necessity hinders the efficiency and increases the cost of deployment of the field system.
Two prior art design approaches that use a hermaphroditic cable connector with an identical connector at both ends of the receiver-line cable section, and not requiring a back-to-back connector, have been proposed and tested. The first of these two designs utilizes electrical pins that are not connected to the corresponding conductors in the cable so that the geophone arrays in the two cable sections are not electrically combined. The second such design omits these electrical pins entirely. Both of these approaches have suffered from a serious shortcoming that severely affects data quality and operational cost: electrical leakage caused by water entering the connector body or the empty pin sockets. (The sockets are required when, during a subsequent deployment of the cable section, the same connector is connected to a RAM.)
An object of the present invention, therefore, is to provide a universal seismic cable connector of hermaphroditic design that can be semi-permanently affixed to both ends of receiver-line cable sections and to RAMs such that two cable sections may be joined together and connected to and between two RAMs, without regard for the direction of the cable sections and without the need of a back-to-back connector or other adapter between the two cable sections; and such that when so connected, all of the geophone channels in the two cable sections are electrically blocked at the juncture of the two cable sections, but also such that each cable section's own geophone channels are electrically connected to its RAM. In the context of this invention, “semi-permanently affixed” means that the connector may be removed and replaced only with the use of tools and materials.
Another object of the present invention is to provide a universal seismic cable connector of hermaphroditic design that can be semi-permanently affixed to both ends of a receiver-line cable section and that allows the cable section to be directly connected in either direction to another receiver-line cable section, to a base-line cable section or to a jumper cable section; or to be connected between any pair of RAMs, between any pair of BLUs, between a RAM and a BLU or between any other pair of data acquisition, processing, communication, recording, control or other modules of a seismic data acquisition system.
A further object of the invention is to provide a universal seismic cable connector of hermaphroditic design that can be semi-permanently affixed to both ends of a base-line cable section and that allows the cable section to be directly connected in either direction to another base-line cable section, to a receiver-line cable section or to a jumper cable section; or to be connected between any pair of BLUs, between a BLU and a recording unit or control unit, or between any other pair of data acquisition, processing, communication, recording, control or other units and modules of a seismic data acquisition system.
A further object of the invention is to provide a universal seismic cable connector that does not require use of a back-to-back connector or other adapter for any cable-to-cable or cable-to-module connections.
A further object is to provide such a universal seismic cable connector that is not subject to water penetration and consequent electrical leakage.
A further object of the invention is to provide a universal seismic cable connector that is robust and able to reliably and repeatedly withstand compressional, tensional, shear and vibrational forces normally encountered in field utilization, without sustaining damage, under the very wide range of field conditions encountered by seismic field crews operating around the world in all climates, terrains, and exposure to water including saline water.
A further object is to provide such a universal seismic cable connector that is manufacturable at competitive cost and is thus affordable by industry standards; and to further reduce equipment cost by reducing the number of connector and adapter types, as well as the absolute number of connectors and adapters, required to conduct seismic data acquisition projects.
A further object is to provide a universal seismic cable connector that is easy to manually connect and disconnect and that may not be physically connected in a manner that does not provide correct connection of the intended conductors.
A still further object of the invention is to allow seismic network modules that may be able to perform multiple functions to be inter-connectable with either base-line, receiver-line or jumper cable sections thereby maximizing flexibility and efficiency of equipment utilization.